Speaking from the historic Royal Castle in Warsaw, Poland, President Joe Biden opened his speech by quoting Pope John Paul II, the first Polish pope elected in history.

“Be not afraid,” Biden, America’s second Catholic president said, quoting the Polish Pope's papal installation Mass from 1978, warning of a long fight ahead against Russia.

“In this battle, we need to be clear-eyed," Biden said. "This battle will not be won in days and months either. We need to steel ourselves for the long fight ahead." 

"It was here in Warsaw when a young refugee who fled her home country from Czechoslovakia, was under Soviet domination, came back to speak and stand in solidarity with dissidents," Biden said. "Her name was Madeleine Korbel Albright."

"She became one of the most ardent supporters of democracy in the world," Biden said. "She was a friend with whom I served. America's first woman secretary of state. She passed away three days ago."

"She fought her whole life for essential democratic principles, and now, in the perennial struggle for democracy and freedom, Ukraine and its people are on the front lines, fighting to save their nation." Biden said. "And their brave resistance is part of a larger fight for essential democeratic principles that unite all free people: The rule of law, fair and free elections, the freedom to speak, to write and to assemble, the freedom to worship as one chooses, freedom of the press. These principles are essential in a free society."

Biden offered a message to Ukraine people: "My message to the people of Ukraine is a message I delivered today to Ukraine's foreign minister and defense minister, who I believe are here tonight: We stand with you, period.”

Turning his ire toward Russia and its leader, Vladimir Putin, the president decried the country’s autocratic nature, saying it has “strangled” democracy at home and abroad.

"The battle for democracy did not conclude with the end of the Cold War,” Biden said. “Today, Russia has defeated democracy and sought to do so elsewhere, not only in its homeland.”

Biden said that Russia’s actions threaten to bring about “decades of war.”

“Putin has the gall to claim he’s de-Nazifying Ukraine,” the president continued, referencing Ukrainian President Volodymyr Zelenskyy’s Jewish heritage. “It’s a lie. It’s just cynical. He knows that. And It’s obscene.”

Paraphrasing President Abraham Lincoln, Biden said we must have faith that “right makes might,” blasting the fact that “Putin has the audacity to believe that … might will make right.”

“There's simply no justification or provocation for Russia's choice for war,” Biden said, mentioning the numerous off-ramps and diplomatic paths the U.S. and other countries offered Putin. "It’s an example of one of the oldest human impulses: using brute force and disinformation to satisfy a craving for absolute power and control."

Now, Biden said, the sanctions the U.S. and other allies have placed on Russia have “reduced the Ruble to rubble.”

“It’s true,” Biden added, referencing the exchange rate between the United States Dollar and the Ruble — Currently, $1 USD is worth more than 100 Rubles.

“A criminal wants to portray NATO enlargement as an imperial project aimed at destabilizing Russia,” Biden said of Putin. “Nothing is further from the truth. NATO is a defensive alliance." 

“It's Putin, it's Vladimir Putin who's to blame, period,” Biden said about the sanctions.

The president also issued a stern warning to Putin, angrily saying: ”Don’t even think about moving on one single inch of NATO territory."

Biden made clear that "American forces are not in Europe to engage in conflict with Russian forces, American forces are here to defend NATO allies," but added: "We have a sacred obligation under Article 5 to defend each and every inch of NATO territory with the full force of our collective power."

The president's speech came as explosions rocked Lviv, a major Ukrainian city near the border with Poland.

The president called the war a "strategic failure for Russia already," but noted that would come as no comfort to those who have lost loved ones in the conflict.

"Notwithstanding the brutality of Vladimir Putin, let there be no doubt that this war has already been a strategic failure for Russia already," Biden said. "Having lost children myself, I know that's no solace to the people who have lost family. But he, Putin, thought Ukrainians would roll over and not fight."

"Not much of a student of history," Biden quipped. "Instead, Russian forces have met their match with brave and stiff Ukrainian resistance. Rather than breaking Ukrainian resolve, Russia's brutal tactics have strengthened the resolve."

"Rather than driving NATO apart, the West is more united than it has ever been," Biden continued. "Russia wanted less of a NATO presence on his border, but now he has a stronger presence, a larger presence, with over 100,000 American troops here, along with all the other members of NATO."

"Russia has managed to cause something I'm sure he never intended: the democracies of the world are revitalized in unity and purpose found in months that weds once taken years to accomplish," Biden added.

Biden referenced some of the Ukrainian refugees he met earlier Saturday, noting that he "didn't have to speak the language or understand the language to feel the emotion."

"All the world's democracies have a responsibility to help," Biden said, adding that the U.S. will meet that responsibility. 

 More than 3.7 million have fled the country, with a total of 10 million people in Ukraine driven from their homes, according to the United Nations. More than 2.2 million people from Ukraine have fled to Poland. The U.S. announced earlier this week it will take in as many as 100,000 Ukrainian refugees.

Biden said that the U.S. will aid Europe in helping their reliance on Russian energy, saying that the continent's supplies being at "the whims of a tyrant ... must end."

"We must commit now to be in this fight for the long haul," Biden said. It will not be easy, there will be costs, but it’s the price we have to pay.”

Biden also spoke directly to Russia's people, a tactic similar to one taken by Zelenskyy throughout the invasion.

"You, the Russian people, are not our enemy," Biden said. "This war is not worthy of you, the Russian people."

"Vladimir Putin's aggression have cut you, the Russian people, off from the rest of the world," the president said to the Russian people. "And it's taking Russia back to the 19th century. This is not who you are."

Biden ended his speech with some of his strongest rhetoric yet toward Putin: "For God sake, this man cannot remain in power."

A White House official later clarified that the president was not calling for a regime change in Russia, but rather was emphasizing that Putin cannot use his position to threaten neighboring countries.

“The President’s point was that Putin cannot be allowed to exercise power over his neighbors or the region," the official said. "He was not discussing Putin’s power in Russia, or regime change.”

The remarks came just hours after Biden called Putin a "butcher" after meeting with Ukrainian refugees, and days after the U.S. officially declared that Russian forces have committed war crimes in Ukraine.

The president's powerful speech capped off a consequential four-day trip to Europe, in which he sought to reaffirm the strength of NATO and the United States' relationships with allied nations, as well as unveil a new tranche of punishments on Russia for its invasion of Ukraine.

Read more about Biden's trip to Europe and the latest updates from Ukraine in our live blog.